A radio communication technology that has been significantly developed in the field of broadcasting and communication has sequentially overcome problems of interruption and an update non-allowable region unique to radio, and has launched into the field of control and observation requiring high reliability in a communication line in comparison with a phone call, and listening and watching by improving reliability of a communication line. Especially in a social infrastructure device, reliability of communication means is higher than a device for general consumers, but application of a radio technology to the communication means has been examined in this field. In such a social infrastructure device, there is a need for high reliability in communication quality.
In a radio device, electromagnetic waves that propagate in free space are used as a transmission medium of communication, but the frequency of the electromagnetic waves that can wirelessly propagate in real space ranges from 300 MHz to 3 GHz. In the frequency which is equal to or less than the aforementioned range, radiation efficiency of radio waves in the air is significantly decreased, whereas in the frequency which is equal to or greater than the aforementioned range, since electromagnetic wave energy is greatly attenuated due to a scattering phenomenon arising from interruption, reflection or diffraction occurring when the radio waves propagate in the air, it is difficult to maintain the distance between transmission and reception points. Thus, communication is performed in only a nearby region, and it is difficult to realize radio communication in the broad sense. At present, an operation frequency of a general-purpose digital device is increased to from several hundreds of MHz to several GHz, and it is possible to introduce a digital circuit to a device that performs radio communication.
As the radio communication technology using such a digital circuit, PTL 1 describes a technology in which in communication using electromagnetic waves on which information received from a transmission side through different paths is superimposed, means for increasing the amount of the information by using the paths which have been increased in number or improving transmission reliability of the information digitizes information to be transmitted, performs quadrature modulation on a digitized signal using a special symbol, and transmits the processed signal, and a reception side separates the received signals at once using the symbol, so that the amount of information is increased or the transmission reliability of the information is increased.